In recent years, there have been proposed and developed various variable valve timing control systems each employing a phase converter, such as a hydraulically-operated vane-type timing variator. A hydraulically-operated vane-type timing variator has been disclosed in Japanese Patent Provisional Publication No. 2002-30908 (hereinafter is referred to as “JP2002-30908”). In the hydraulically-operated vane-type variable valve timing control (VTC) device disclosed in JP2002-30908, a vane member is fixedly connected to a camshaft end and rotatably enclosed in a cylindrical housing of a timing pulley whose opening ends are enclosed with front and rear covers. The front cover, the cylindrical housing, and the rear cover are integrally connected to each other by means of a plurality of bolts. Four phase-advance hydraulic chambers and four phase-retard hydraulic chambers are defined by four frusto-conical partition walls (four shoes) radially inwardly extending from the inner periphery of the cylindrical housing and four blades (four vanes) of the vane member. The rear plate is formed integral with a timing-chain sprocket (or a timing-belt pulley), which serves as a rotary member driven in synchronism with rotation of an engine crankshaft. The first one of the four vane blades has an axial bore that slidably accommodating therein a lock pin (or a lock piston). On the other hand, the front plate has a lock-pin hole formed in its axially inside end. Depending on an engine operating condition, the lock pin is selectively engaged with or disengaged from the lock-pin hole. For instance, during an engine starting period, the lock pin is brought into engagement with the lock-pin hole, thus constraining rotary motion (free rotation) of the vane member relative to the cylindrical housing and consequently preventing the camshaft from rotating relative to the crankshaft. As a result, the vane member is held at a phase-retarded angular position suited to the engine starting period. Additionally, in the hydraulically-operated vane-type VTC device disclosed in JP2002-30908, the circumferential width L1 of the first vane blade, having the axial bore slidably accommodating therein the lock pin, and the circumferential width L2 of the second vane blade, diametrically opposing the first vane blade, are both dimensioned to be wider than each of circumferential widths L3 and L4 of the remaining vane blades (that is, L1, L2>L3, L4). Such setting of the circumferential widths L1-L4 is effective to ensure a comparatively great phase change of the vane member relative to the cylindrical housing without causing rotational unbalance of the vane member having three or more blades.